Protein kinases are enzymatic components of the signal transduction pathways which catalyze the transfer of the terminal phosphate from ATP to the hydroxy group of tyrosine, serine and/or threonine residues of proteins. Thus, compounds which inhibit protein kinase functions are valuable tools for assessing the physiological consequences of protein kinase activation. The overexpression or inappropriate expression of normal or mutant protein kinases in mammals has been a topic of extensive study and has been demonstrated to play a significant role in the development of many diseases, including diabetes, angiogenesis, psoriasis, restenosis, ocular diseases, schizophrenia, rheumatoid arthritis, atherosclerosis, cardiovascular disease and cancer. The cardiotonic benefits of kinase inhibition has also been studied. In sum, inhibitors of protein kinases have particular utility in the treatment of human and animal disease.
The fms-like tyrosine kinase 3 (FLT3) ligand (FLT3L) is one of the cytokines that affects the development of multiple hematopoietic lineages. These effects occur through the binding of FLT3L to the FLT3 receptor, also referred to as fetal liver kinase-2 (flk-2) and STK-1, a receptor tyrosine kinase (RTK) expressed on hematopoietic stem and progenitor cells. The FLT3 gene encodes a membrane-bound RTK that plays an important role in proliferation, differentiation and apoptosis of cells during normal hematopoiesis. The FLT3 gene is mainly expressed by early myeloid and lymphoid progenitor cells. See McKenna, Hilary J. et al. Mice lacking flt3 ligand have deficient hematopoiesis affecting hematopoietic progenitor cells, dendritic cells, and natural killer cells. Blood. June 2000; 95: 3489-3497; Drexler, H. G. and H. Quentmeier (2004). “FLT3: receptor and ligand.” Growth Factors 22(2): 71-3.
The ligand for FLT3 is expressed by the marrow stromal cells and other cells and synergizes with other growth factors to stimulate proliferation of stem cells, progenitor cells, dendritic cells, and natural killer cells.
Hematopoietic disorders are pre-malignant disorders of these systems and include, for instance, the myeloproliferative disorders, such as thrombocythemia, essential thrombocytosis (ET), angiogenic myeloid metaplasia, myelofibrosis (MF), myelofibrosis with myeloid metaplasia (MMM), chronic idiopathic myelofibrosis (IMF), and polycythemia vera (PV), the cytopenias, and pre-malignant myelodysplastic syndromes. See Stirewalt, D. L. and J. P. Radich (2003). “The role of FLT3 in haematopoietic malignancies.” Nat Rev Cancer 3(9): 650-65; Scheijen, B. and J. D. Griffin (2002). “Tyrosine kinase oncogenes in normal hematopoiesis and hematological disease.” Oncogene 21(21): 3314-33.
Hematological malignancies are cancers of the body's blood forming and immune systems, the bone marrow and lymphatic tissues. Whereas in normal bone marrow, FLT3 expression is restricted to early progenitor cells, in hematological malignancies, FLT3 is expressed at high levels or FLT3 mutations cause an uncontrolled induction of the FLT3 receptor and downstream molecular pathway, possibly Ras activation. Hematological malignancies include leukemias, lymphomas (non-Hodgkin's lymphoma), Hodgkin's disease (also called Hodgkin's lymphoma), and myeloma—for instance, acute lymphocytic leukemia (ALL), acute myeloid leukemia (AML), acute promyelocytic leukemia (APL), chronic lymphocytic leukemia (CLL), chronic myeloid leukemia (CML), chronic neutrophilic leukemia (CNL), acute undifferentiated leukemia (AUL), anaplastic large-cell lymphoma (ALCL), prolymphocytic leukemia (PML), juvenile myelomonocyctic leukemia (JMML), adult T-cell ALL, AML with trilineage myelodysplasia (AML/TMDS), mixed lineage leukemia (MLL), myelodysplastic syndromes (MDSs), myeloproliferative disorders (MPD), multiple myeloma, (MM) and myeloid sarcoma. See Kottaridis, P. D., R. E. Gale, et al. (2003). “Flt3 mutations and leukaemia.” Br J Haematol 122(4): 523-38. Myeloid sarcoma is also associated with FLT3 mutations. See Ansari-Lari, Ali et al. FLT3 mutations in myeloid sarcoma. British Journal of Haematology. 2004 September 126(6):785-91.
Mutations of FLT3 have been detected in about 30% of patients with acute myelogenous leukemia and a small number of patients with acute lymphomatic leukemia or myelodysplastic syndrome. Patients with FLT3 mutations tend to have a poor prognosis, with decreased remission times and disease free survival. There are two known types of activating mutations of FLT3. One is a duplication of 4-40 amino acids in the juxtamembrane region (ITD mutation) of the receptor (25-30% of patients) and the other is a point mutation in the kinase domain (5-7% of patients). The mutations most often involve small tandem duplications of amino acids within the juxtamembrane domain of the receptor and result in tyrosine kinase activity. Expression of a mutant FLT3 receptor in murine marrow cells results in a lethal myeloproliferative syndrome, and preliminary studies (Blood. 2002; 100: 1532-42) suggest that mutant FLT3 cooperates with other leukemia oncogenes to confer a more aggressive phenotype.
Specific inhibitors of FLT3 kinase present an attractive target for the treatment of hematopoietic disorders and hematological malignancies.
FLT3 kinase inhibitors known in the art include AG1295 and AG1296; Lestaurtinib (also known as CEP 701, formerly KT-5555, Kyowa Hakko, licensed to Cephalon); CEP-5214 and CEP-7055 (Cephalon); CHIR-258 (Chiron Corp.); EB-10 and IMC-EB10 (ImClone Systems Inc.); GTP 14564 (Merk Biosciences UK). Midostaurin (also known as PKC 412 Novartis AG); MLN 608 (Millennium USA); MLN-518 (formerly CT53518, COR Therapeutics Inc., licensed to Millennium Pharmaceuticals Inc.); MLN-608 (Millennium Pharmaceuticals Inc.); SU-11248 (Pfizer USA); SU-11657 (Pfizer USA); SU-5416 and SU 5614; THRX-165724 (Theravance Inc.); AMI-10706 (Theravance Inc.); VX-528 and VX-680 (Vertex Pharmaceuticals USA, licensed to Novartis (Switzerland), Merck & Co USA); and XL 999 (Exelixis USA). The following PCT International Applications and U.S. patent applications disclose additional kinase modulators, including modulators of FLT3: WO 2002032861, WO 2002092599, WO 2003035009, WO 2003024931, WO 2003037347, WO 2003057690, WO 2003099771, WO 2004005281, WO 2004016597, WO 2004018419, WO 2004039782, WO 2004043389, WO 2004046120, WO 2004058749, WO 2004058749, WO 2003024969 and U.S. Patent Application No. 20040049032.
See also Levis, M., K. F. Tse, et al. 2001 “A FLT3 tyrosine kinase inhibitor is selectively cytotoxic to acute myeloid leukemia blasts harboring FLT3 internal tandem duplication mutations.” Blood 98(3): 885-7; Tse K F, et al. Inhibition of FLT3-mediated transformation by use of a tyrosine kinase inhibitor. Leukemia. 2001 July; 15(7): 1001-10; Smith, B. Douglas et al. Single-agent CEP-701, a novel FLT3 inhibitor, shows biologic and clinical activity in patients with relapsed or refractory acute myeloid leukemia Blood, May 2004; 103: 3669-3676; Griswold, Ian J. et al. Effects of MLN518, A Dual FLT3 and KIT Inhibitor, on Normal and Malignant Hematopoiesis. Blood, July 2004; [Epub ahead of print]; Yee, Kevin W. H. et al. SU5416 and SU5614 inhibit kinase activity of wild-type and mutant FLT3 receptor tyrosine kinase. Blood, September 2002; 100: 2941-294; O'Farrell, Anne-Marie et al. SU11248 is a novel FLT3 tyrosine kinase inhibitor with potent activity in vitro and in vivo. Blood, May 2003; 101: 3597-3605; Stone, R. M. et al. PKC 412 FLT3 inhibitor therapy in AML: results of a phase II trial. Ann Hematol. 2004; 83 Suppl 1:S89-90; and Murata, K. et al. Selective cytotoxic mechanism of GTP-14564, a novel tyrosine kinase inhibitor in leukemia cells expressing a constitutively active Fms-like tyrosine kinase 3 (FLT3). J Biol Chem. 2003 Aug. 29; 278(35):32892-8; Levis, Mark et al. Novel FLT3 tyrosine kinase inhibitors. Expert Opin. Investing. Drugs (2003) 12(12) 1951-1962; Levis, Mark et al. Small Molecule FLT3 Tyrosine Kinase Inhibitors. Current Pharmaceutical Design, 2004, 10, 1183-1193.